Protective damper for gas exhaust duct

ABSTRACT

A damper that is normally biased toward open position against the pressure of air flowing through the damper and rapidly closed by the increase of such pressure resulting when pressure exteriorly of the damper abruptly drops to a predetermined level. The damper comprises a plurality of parallel blades mounted on parallel axes and coupled to each other for movement between a closed position with the blades lying generally in a vertical plane across the damper and normally open position with the blades lying in parallel spaced planes inclined into the air flow. Means are connected to the blades for biasing them inwardly toward open position against the pressure interiorly of the damper caused by the air flow which tends to swing the blades in an outward direction toward closed position. When the atmospheric pressure on the outside of the damper drops, as by the presence of the negative phase of a tornado, the damper closes immediately.

[451 Sept. 24, 1974 PROTECTIVE DAMPER FOR GAS EXHAUST DUCT [75]Inventor: Raymond L. Alley, Toledo, Ohio [73] Assignee: The AmericanWarming &

Ventilating, lnc., Toledo, Ohio 22 Filed: Nov. 9, 1972 21 Appl. No.:305,086

[52] US. Cl 98/110, 98/32, 98/95, 98/119, l37/512.l, 137/520, 137/521[51] Int. Cl F24f 13/16 [58] Field of Search 98/110, 119, 121 A, 121 R,98/107, 95,116, 32; 49/31, 89; 160/5, 517; 137/521, 512.1, 493.1, 520

[56] References Cited UNITED STATES PATENTS 426,628 4/1890 Smith 137/520505,238 9/1893 Smith 137/520 Roach 98/119 3,584,567 6/1971 3,604,4589/1971 Silvey 98/110 3,668,999 6/1972 Alley et al. 98/119 PrimaryExaminer-Meyer Perlin Assistant Examiner-Paul Devinsky Attorney, Agent,or Firm-Henry K. Leonard [5 7] ABSTRACT A damper that is normally biasedtoward open position against the pressure of air flowing through thedamper and rapidly closed by the increase of such pressure resultingwhen pressure exteriorly of the damper abruptly drops to a predeterminedlevel. The damper comprises a plurality of parallel blades mounted onparallel axes and coupled to each other for movement between a closedposition with the blades lying generally in a vertical plane across thedamper and normally open position with the blades lying in parallelspaced planes inclined into the air flow. Means are connected to theblades for biasing them inwardly toward open position against thepressure interiorly of the damper caused by the air flow which tends toswing the blades in an outward direction toward closed position. Whenthe atmospheric pressure on the outside of the damper drops, as by thepresence of the negative phase of a tornado, the damper closesimmediately.

3 Claims, 5 Drawing Figures PAIENIEDSEPZMW 3.837.268

7? m FIE-1- 3 Eli-3+ FIE-z- PROTECTIVE DAMPER FOR GAS EXHAUST DUCTBACKGROUND OF THE INVENTION In many types of commercial and industrialbuildings it is necessary to provide fan-actuated exhaust systems tocarry away contaminated air from within the establishment and, in manyinstances, the exhaust systems are also utilized for removingparticulate material from the areas of operation for the protection ofpersons in the areas. Exhaust systems of this type are equipped withfiltering media in order to filter the contaminants out of the exhaustair before it is discharged to atmosphere. When such an arrangementexists in a building in the area of the country which is subject totornados, an unexpected event frequently occurs.

Because of the forced draft exhaust from the building, when the negativephase of a tornado passes the building, the sudden drop in atmosphericpressure results in an immediate increase in the relative pressurebetween the interior and the exterior of the building and thus theapplication of an instantaneously higher pressure to the filters whichmay be placed in the exhaust system. As a result the filters frequentlyare blown out of the exhaust system and destroyed or severely damaged.

It is therefore the principal object of the instant invention to providea protective damper for an exhaust gas system which will closeimmediately upon the existence of a predetermined low pressureexteriorly of the building thus preventing a sufficient build-up of thepressure differential to destroy the filtering media.

Attempts have been made to accomplish this objective by the utilizationof dampers which are closed by relatively rapidly actuated mechanicalmeans such as the release of pretensioned springs or the energization ofpower means of one kind or another but most of .these attempts havefailed because they are not rapid enough in actuation or because theyhave been so designed as to operate contrary to the instantaneouslyincreased pressure differential which results when the negative phase ofthe tornado is present.

In contrast to these previous attempts, the present inventioncontemplates the utilization of the instantaneously increased pressuredifferential, itself, to close the protective damper.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary vertical view inelevation of a protective damper embodying the invention taken from theinner side of the damper and showing a gas duct in cross-section;

FIG. 2 is a fragmentary side view in elevation taken from the positionindicated by the line 22 of FIG. 1;

FIG. 3 is a vertical sectional view taken along the line 3-3 of FIG. 1;

FIG. 4 is a fragmentary side view, partly in section and partly inelevation, illustrating details of a damper embodying the invention andshown on an enlarged scale; and

FIG. 5 is a fragmentary, horizontal sectional view taken along the line55 of FIG. 4 and shown on a still further enlarged scale.

DESCRIPTION OF PREFERRED EMBODIMENT The illustrated embodiment of theinvention comhaust gases prior to their discharge in atmosphere. Al-

though no such filter is shown in the drawings, it is assumed that theduct 11 is so equipped.

The frame 10 mounts a plurality of transversely extending damper blades12 each of which is pivotally mounted on one of a series of spacedparallel axles 13, the axles 13 being journalled in side members 14 ofthe frame 10. The axles 13 are spaced vertically from each other adistance such that when the damper blades 12 are all swung to closedposition (FIG. 4) each of the blades 12 overlaps the axle 13 of anadjacent lower blade and the lower-most one of the blades 12 engages asealing strip 15 (FIG. 3) extending along the bottom of the frame 10.Thus when the blades 12 are swung to closed position they all lie insubstantially the same vertical plane and the duct 11 is closed so thatgases normally being exhausted, as indicated by the arrows in FIGS. 2,3, and 4, can no longer flow out of the duct 1 1.

All of the blades 12 are coupled to each other for simultaneous angularmovements by a vertically extending link 16 which is pivotally attachedto the ends of lever arms 17, each of the arms 17 being pinned orotherwise secured on one of the blade axles 13. The link 16 alsofunctions as a stop means to limit the inward angular movement of theblades 12 and thus the maximum open position of the damper, the upperend of the link 16 engaging a stop 18 to accomplish this objective. Thestp 18 is mounted on a bracket 19 and is vertically adjustable in orderto vary the stop position and thus the maximum angle to which the blades12 can be opened.

In the illustrated embodiment of the invention, means for biasing thedamper blades 12 inwardly toward their open position are illustrated ascomprising constant tension coil springs 20 of which two are shown. Eachof the springs 20 comprises a drum 21 around which a ribbon 22 is woundin such fashion that tension is applied to the ribbon 22 seeking torewind it on the drum 21. The free end of the ribbon 22 is connected bya clamp 23 to a finger 24 and the finger 24 is mounted by a lock-screw25 for movement along a slot 26 in a lever 27. The lever 27, in turn, iswelded, rivoted, pinned, or otherwise secured on the end of therespective one of the blade axles 13. By sliding the lock-screw 25 andthe finger 24 along the slot 26, the moment of force applied by thespring 20 to the respective blade axle and through the link 16 to all ofthe blades 12 can be varied as desired.

While it might be possible to predetermine the final positions of thestop 18 to limit the inward movement of the blades 12 into the flow ofgases and to preadjust the positions of the fingers 24 in their levers27, to establish the bias applied to the blades 12, in most instancesthese adjustments are made after the installation of the damperembodying the invention. The degree of adjustment of both of thesevariable items will be determined by the precise volume and rate of airflow out of the damper, by calculating the pressure applied over theprojected area of the blades 12 when they stand in their inner, openposition, inclined into the flow of gases.

The tension applied by the springs 22 to the blades biases them towardtheir open, inclined positions against the force applied to the blades12 by the pressure created by the exhaust fans. Under normal operatingconditions the balance of forces is such that the force applied to theblades 12 by the exhaust gases is insufficient to swing them to theirclosed positions and the blades are held in the normal operatingposition illustrated in FIGS. 2 and 3 by the tension applied thereto bythe biasing means, i.e., the springs 20 and their mechanicalconnections.

When an abrupt drop in atmospheric pressure occurs, as for example bythe passage of the negative phase of a tornado, the relative pressuresbetween the inner side and outer side of the blades 12 increasesinstantaneously. The absence of positive pressure on the external sideof the blades 12 thus results in the normal airflow pressure beingsufficient to abruptly swing the blades 12 to their closed positionalmost instantaneously and rapidly enough so that the otherwise occuringblow-out" of the filter in the duct does not occur. Upon restoration ofa normal exterior atmospheric pressure, the biasing springs 20 onceagain swing the blades 12 to their predetermined open position andnormal operation follows.

What I claim is:

1. A protective damper for a gas exhaust opening, said dampercomprising, in combination,

a. an open rectangular frame defining an exhaust opening to atmosphere,

b. a plurality of rectangular essentially planar damperblades,-extending across such opening, said blades being mounted onparallel, spaced axes extending along corresponding edges thereof forangular movement between closed position with all of said blades lyinggenerally in a plane transverse to the flow of gas through said frameand with said blades engaging each other and open position with all ofsaid blades swung inwardly against such flow of gas and lying in spacedparallel planes inclined into such gas flow,

(2. means coupling said blades for movement to gether,

d. means biasing said blades inwardly away from closed position to openposition against such flow of gas and the force of gravity, and

e. wherein said damper blades are responsive solely to atmosphericpressure drop to move to closed position.

2. A damper according to claim 1 in which the means for biasing theblades comprises a constant tension spring means and which hasadjustable force applying means.

3. A damper according to claim 1 and stop means for limiting the angularmovement of said blades away from closed position to a predeterminedmaximum.

1. A protective damper for a gas exhaust opening, said dampercomprising, in combination, a. an open rectangular frame defining anexhaust opening to atmosphere, b. a plurality of rectangular essentiallyplanar damper blades, extending across such opening, said blades beingmounted on parallel, spaced axes extending along corresponding edgesthereof for angular movement between closed position with all of saidblades lying generally in a plane transverse to the flow of gas throughsaid frame and with said blades engaging each other and open positionwith all of said blades swung inwardly against such flow of gas andlying in spaced parallel planes inclined into such gas flow, c. meanscoupling said blades for movement together, d. means biasing said bladesinwardly away from closed position to open position against such flow ofgas and the force of gravity, and e. wherein said damper blades areresponsive solely to atmospheric pressure drop to move to closedposition.
 2. A damper according to claim 1 in which the means forbiasing the blades comprises a constant tension spring means and whichhas adjustable force applying means.
 3. A damper according to claim 1and stop means for limiting the angular movement of said blades awayfrom closed position to a predetermined maximum.